To develop definitive interventional strategies to prevent mother to infant transmission of HIV virus type 1 and to prevent disease progress in HIV-1 infected children. It is essential to understand the host and viral factors which are the major determinants of perinatal transmission (intrauterine and intrapartum), virulence and disease expression. Susceptibility of fetal leukocyte subsets, in particular monocytes/macrophages, dendritic cells, and stem cells to HIV-1 infection and viral tropism for these different subsets have not been studied. Identifying factors that affect the rate of transmission may lead to the initiation of specific strategies. The investigators hypothesize that perinatal transmission of HIV-1 from mother to child is affected by the innate biological properties of these cell subsets and their susceptibility to HIV-1 infection. We further hypothesize that the immonopathogenesis of HIV-1 infection in infants is, in part, determined by the interaction of these subsets with the virus.